Airfoil last chance screen utilizing EDM and AFM

Abstract

A method of manufacturing a last chance screen for an aircraft engine includes forming an array of holes through a metal sheet with a wire electrode using electrical discharge machining. The array of holes comprises a plurality of holes. Each hole of the plurality of holes comprises a first end and a second end and is surrounded by a wall section such that the last chance screen is defined by the plurality of holes and the plurality of wall sections. The first and second end of each hole are widened by either applying a flow of an abrasive flow medium to the array of holes in two directions or using a conical sinker electrode on either side of the metal sheet. Shaping the first and second end of each hole results in an airfoil-shaped cross-section of each wall section.

The invention claimed is: 
     
       1. A method of manufacturing a last chance screen for an aircraft engine, the method comprising:
 forming an array of holes through a metal sheet with a wire electrode using electrical discharge machining, wherein:
 the array of holes comprises a plurality of holes; 
 each hole of the plurality of holes extends from a first end to a second end; and 
 each hole is surrounded by one or more wall sections such that the last chance screen is defined by the plurality of holes and the plurality of wall sections; 
 
 shaping the first end of each hole by applying a flow of an abrasive flow medium to the array of holes in a first direction, such that the first end of each hole is widened by the flow of the abrasive flow medium and a portion of the wall section adjacent to the first end of each hole has a first convex curvature with respect to the hole; and 
 shaping the second end of each hole by applying a flow of the abrasive flow medium to the array of holes in a second direction which is opposite to the first direction, such that the second end of each hole is widened by the flow of the abrasive flow medium and a portion of the wall section adjacent to the second end of each hole has a second convex curvature with respect to the hole; 
 wherein shaping the first end of each hole and shaping the second end of each hole results in an airfoil-shaped cross-section of each wall section. 
 
     
     
       2. The method of  claim 1 , wherein the metal sheet is formed of a stainless steel alloy. 
     
     
       3. The method of  claim 2 , wherein the stainless steel alloy is selected from the group comprising: grade 304 stainless steel and grade 316L stainless steel. 
     
     
       4. The method of  claim 1 , wherein the metal sheet is formed of an Inconel® alloy. 
     
     
       5. The method of  claim 1 , wherein each wall section has a diameter of approximately 0.004 inches at a widest point of the wall section. 
     
     
       6. The method of  claim 1 , wherein each hole has a diameter of approximately 0.005 inches at a narrowest point of the hole. 
     
     
       7. The method of  claim 1 , wherein the plurality of holes are arranged in the metal sheet such that the array of holes forms a square grid. 
     
     
       8. The method of  claim 1 , wherein the plurality of holes are arranged in the metal sheet such that the array of holes forms a hexagonal grid. 
     
     
       9. The method of  claim 1 , wherein the first convex curvature is greater than the second convex curvature. 
     
     
       10. The method of  claim 1 , wherein the second convex curvature is greater than the first convex curvature. 
     
     
       11. The method of  claim 1 , wherein the abrasive flow medium comprises a low-viscosity liquid and a diamond powder abrasive. 
     
     
       12. The method of  claim 1 , wherein the plurality of wall sections comprises:
 a plurality of first members extending in a first direction; and 
 a plurality of second members extending in a second direction such that each second member of the plurality of second members intersects at least one first member of the plurality of second members; 
 wherein:
 each hole is surrounded by two first members and two second members; 
 each hole forms a square opening at the first end and the second end; and 
 each first member and each second member have an airfoil-shaped cross-section. 
 
 
     
     
       13. A method of manufacturing a last chance screen for an aircraft engine, the method comprising:
 forming an array of holes through a metal sheet with a wire electrode using electrical discharge machining, wherein:
 the array of holes comprises a plurality of holes; 
 each hole of the plurality of holes extends from a first end to a second end; and 
 each hole is surrounded by a wall section such that the last chance screen is defined by the plurality of holes and the plurality of wall sections; 
 
 shaping the first end of each hole with a first conical sinker electrode using electrical discharge machining, such that the first end of each hole is widened by the electrical discharge machining and a portion of the wall section adjacent to the first end of each hole has a first convex curvature with respect to the hole; and 
 shaping the second end of each hole with a second conical sinker electrode using electrical discharge machining, such that the second end of each hole is widened by the electrical discharge machining and a portion of the wall section adjacent to the second end of each hole has a second convex curvature with respect to the hole; 
 wherein shaping the first end of each hole and shaping the second end of each hole results in an airfoil-shaped cross-section of each wall section. 
 
     
     
       14. The method of  claim 13 , wherein the wire electrode has a constant diameter between 0.001 inches to 0.25 inches. 
     
     
       15. The method of  claim 14 , wherein the wire electrode has a constant diameter of 0.005 inches. 
     
     
       16. The method of  claim 13 , wherein the first conical sinker electrode and the second conical sinker electrode each have a diameter of between 0.001 inches to 0.25 inches. 
     
     
       17. The method of  claim 16 , wherein the first conical sinker electrode widens the first end of each hole by 0.004 inches. 
     
     
       18. The method of  claim 16 , wherein the second conical sinker electrode widens the second end of each hole by 0.004 inches. 
     
     
       19. The method of  claim 13 , wherein a half-cone angle between an end of each wall section and a widest point of each wall section is between 1 degrees to 30 degrees. 
     
     
       20. The method of  claim 19 , wherein the half-cone angle is 5 degrees.